1. Field of the Invention
The present invention concerns novel polymer supported sulfonated catechol ligands which are selective for ions (e.g. Fe.sup.3+) generally at low pH in the presence of other metal ions in aqueous solutions. The ions usually a trivalent ion (e.g. Fe.sup.3+) is subsequently recovered from the polymer by a lowering in pH.
2. Description of the Problem and Related Art
There is a growing need in the relatively new area of environmental inorganic chemistry to design organic ligands in order to selectively remove and recover environmentally and economically important metal ions from aqueous solution. One approach to designing organic ligands for these purposes is to look a biological systems for examples on selective metal ion complexation, see A. Martell, (1959) Organic Sequestering Agents; John Wiley & Sons, Inc.; Chap 8, p.416. Thus, the biomimetic approach has provided an array of organic ligands that fulfill the requirements of high selectivity to certain metal ions, especially for Fe.sup.3+ ion, due to its predisposition for octahedral coordination. See K. N. Raymond, (1990), Coord. Chem. Rev, 105,135 and references therein, T. D. P. Stack et al; (1992), J. Amer. Chem. Soc. 114, 1512; T. D. P. Stack; (1993) J. Amer. Chem. Soc. 115, 6466, and C. G. Pierpont, et al (1994), The Chemistry of Transition Metal Complexes Containing Catechol and Semiquinone Ligands in: Progress in Inorganic Chemistry, Karlin, K. D. (Ed.) John Wiley & Sons Publishers: New York, Vol 41, p. 331.
However, the selective removal and recovery of metal ions from environmental aqueous solutions must be cost-effective. Therefore, the anchoring of these selective ligands to solid supports is mandatory for continual reuse. See A. Warshawsky, (1986), Modern Research in Ion Exchange, in: Ion Exchange: Science and Technology, Rodrigues, A. (Ed.) Martinus Nijhoff Publishers: Dordrecht, 1986, p. 67; and E. Blasius et al; (1967) Chelating Ion Exchange Resins, in: Chelates in Analytical Chemistry; Flaschka, H. A.; Barnard, J. A., Eds: Marcel Decker: New York. In prior polymer pendant ligand chemistry studies, on the synthesis of a polymer bound catechol ligand for non-aqueous solution metal ion complexation is described. See R. H. Fish, et al (1985). Inorg. Chem., 24, 4456; and R. H. Fish et al, (1987) Reactive Polymers 6, 255; The diffusion of the metal ions into the hydrophobic polymer matrix is so important, that it is highly desirable to modify the catechol ligands with a hydrophilic group, such as a sulfonic acid substituent, to increase the kinetics and capacities of metal binding in aqueous solution, while also preventing the catechol ligand from being oxidized to the weaker metal binding O-quinone ligand.
With regard to a previous synthesis of a polymer pendant sulfonated catechol ligand, see M. Griesbach et al (1980) Fresenius Z. Anal. Chem., 302, 109; M. Griesbach et al (1980) Angew. Fresenius Z. Anal, Chem., 302, 181; and M. Griesbach et al (1980) Angew Makromol. Chem. 90, 143. described a number of organic ligands that were chemically bound to 2-3% crosslinked polystyrene-divinylbenzene beads (PS-DVB) via an azo group linkage reaction. Among the many ligands attached using the procedure, the 3,5-disulfonatecatechol ligand (TIRON) was also described. However, the stability of the azo linkage at low pH is suspect. Further, the metal ion selectivity found for the polymer-supported azo-linked TIRON ligand appears different from the present data.
The following references are specific and general of interest:
F. W. Weitl et al, U.S. Pat. No. 4,442,305 disclose monomeric polycatecholamide chelating agents.
R. H. Fish, U.S. Pat. No. 4,552,854 discloses the treatment of a spent catecholated polystyrene to recover arsenic compounds.
R. H. Fish, U.S. Pat. No. 4,604,191 discloses a method of removal of arsenic, vanadium and/or nickel compounds from petroliferous liquids using a catecholated polystyrene polymer.
H. W. Blanch et al, U.S. Pat. No. 5,073,575 disclose the use of a polystyrene polymer having dithiol groups to chelate cadmium ion.
All patents, applications, articles, standards and the like are incorporated herein by reference in their entirety.
None of these references individually or collectively teach or suggest the present invention.
As is seen from the above text, there is a need for a method to selectively remove iron and other ions from aqueous solution having a mixture of metal ions present. The method and polymer having a catechol amide ligand described herein below solve this problem.